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Problem with line noise from Phono preamp

I'm hoping someone has had experience with this problem and can help me: I've been trying to connect my turntable to my B&K AVP3090 preamp using use an outboard phono preamp. I've tried 2 different outboard phono pre's with the same results - they play ok, but there's a very noticable AC line noise issue.

The 2 units in question are a Rolls VP129 tube phono pre, and a Music Hall MMF Phono Pack. Both units are powered by similar 12V AC power transformer.

My turntable works fine through my Rotel RC1070 (which I sold recently), and when I connect it to the B&K through an old Adcom GFP-1 preamp.

Can anyone help with this? thanks in advance.
bdgregory
4 responses Add your response
hifimaniac
508 posts
 
Have you grounded the phono preamp? Sometimes grounding will reduce hum.
jfrech's avatar
jfrech
1,816 posts
 
Sounds more like a grounding issue. Do you have a ground wire from the tonearm to phono stage?

I'm not a expert on this. I hope someone else chimes in on how to trouble shoot this.

If I the ground wire off, I get the same result.
bdgregory OP
1,710 posts
 
Hifimaniac had the solution. I knew enough to make sure the tone arm ground was secure, but since there's no obvious place to ground the phone pre chassis to the B&K, it just didn't occur to me to ground it. I also assumed that the phono chassis would be properly grounded through the RCA outputs to the B&K.
I connected a jumper from the ground pole on the phono to the ground sleeve on the B&K preamp input (ie the outer part of the RCA). It sounds great now, and much better than playing it through the Adcom.

thanks !!
isellstuff
99 posts
 
Your Left, Right, and Ground cables are HITTING each
other! I had the SAME problems with 3 different turntables! You need to seperate them from each other
higher up, and MAKE SURE that NO OTHER CABLES,
are hitting them! That`s what worked for me.
No problems now!
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